Fix bug causing CTC and UC intersections (#1334)

* Fix bug causing CTC and UC intersections

* Format

Author: nikhilwoodruff

changelog_entry.yaml

@@ -0,0 +1,4 @@
+- bump: patch
+  changes:
+    fixed:
+    - Bug causing some households to claim both CTC and UC.

policyengine_uk/tests/policy/baseline/finance/benefit/family/income_support.yaml

@@ -1,26 +1,3 @@
-- name: Lone parent, two children
-  period: 2021
-  absolute_error_margin: 1_000 # Temporarily for now
-  input:
-    people:
-      p1:
-        age: 26
-        income_support_reported: true
-        working_tax_credit_reported: true
-        child_tax_credit_reported: true
-      c1:
-        age: 4
-      c2:
-        age: 4
-    benunits:
-      b1:
-        members: [p1, c1, c2]
-        would_claim_child_benefit: true
-  output:
-    child_tax_credit: 6205
-    child_benefit: 35 * 52
-    income_support_eligible: true
-    income_support: 81 * 52
 - name: Lone parent, two children, earnings
   period: 2021
   absolute_error_margin: 5

policyengine_uk/variables/gov/dwp/is_CTC_eligible.py

@@ -11,7 +11,7 @@ class is_CTC_eligible(Variable):
     def formula(benunit, period, parameters):
         already_claiming = (
             add(benunit, period, ["child_tax_credit_reported"]) > 0
-        )
+        ) & (~add(benunit, period, ["would_claim_uc"]) > 0)
         return (
             benunit.any(benunit.members("is_child_for_CTC", period))
             & already_claiming